F2010B087
Electrically Powered Steering System - Impact of Advanced Functions
Keywords: electrical steering, steering functions, V-model, functional safety
Subject group: B4 and / or E2, may be D3
Electrically Powered Steering 'Belt Drive EPS' is an innovative power-assist system that eliminates the classic connection between steering system and the engine. The assist power of an electric motor is applied directly to the rack with a belt drive and a ball nut mechanism. This novel approach allows higher rack forces than other electrical steering systems. The Belt Drive EPS design allows a more direct steering feel, additional functionalities and optimized fuel efficiency especially in comparison to conventional hydraulic or electric-hydraulic steering systems.
The used electronic control algorithms and the electronic control unit of Belt Drive EPS allow conventional steering functionalities like Inertia Compensation, Active Return and Active Damping (Vehicle Yaw Compensation). Additionally advanced steering features can be categorized in vehicle control features like Pull-drift and Side-wind compensation. Other so called driver coaching features are Lateral Acceleration Feedback, Oversteer & Split-µ-braking- Compensation and Understeer Torque Feedback.
The article describes the impact of these functionalities on the system architecture and demonstrates that the daisy chain of these complex steering functions increases significantly with additional features. This impact on the system design goes along with increased safety requirements, like for Lane Guidance, Lane Departure Warning and Park Assist System what will also implemented.
Along with functional safety norms IEC 61508, ISO 26262 and AUTOSAR a structured Verification and Validation (V&V) model for advanced steering functions will be described. The elected development and validation process allows in accordance with well chosen working tools, the generation of accurate, clear, measureable, feasible and serviceable requirements.
The paper shows an answer how to handle the increased complexity in transferring steering functions between different applications and how to fulfill the request of the marked for a cost and time effective integration.
This abstract is supplemented by a PDF, which can be viewed here.